Ring Catalytic enantioselective meso-epoxid

Complexes of other metals such as gallium, indium, lead, and antimony have also been used as Lewis acids. Catalytic enantioselective meso-epoxide ring-opening reactions using a chiral gallium(III) catalyst (Ga-Li-linked-BINOL) have been reported (Scheme 84).348 The chemical yields are much improved by linking two BINOL units. 

Using the catalytic system described above, the enantioselective opening of meso epoxides could also be pursued. Although many excellent examples of ring-opening of meso epoxides by Sn2 reactions have recently been reported, the reaction planned here is conceptually different [40]. In the SN2 reaction, the path of the incoming nucleophile has to be controlled. In the titanocene-catalyzed reaction, the intermediate radical has to be formed selectively. If an intermediate similar to that invoked in the Bartmann ring-open-... 

Catalytic, enantioselective ring opening of meso epoxides with various alcohols and amines employing a combination of Sc(OTf)3 and 2,2 -bipyridine (3) (10 mol% each) was reported [130]. For both classes of nucleophiles, moderate to high yields and enantioselectivities were obtained with complete anti diastereoselectivity (Scheme 12.50). Aliphatic amines did not give the desired products, presumably due to catalyst inhibition. The PMB-protected diol was converted into the corresponding acyloin by oxidation with almost complete retention of configuration. Alternatively, oxidation with CAN furnished the unprotected diol. 

After Kobayashi spioneering study on theabiUty of (S)-2,2 -bis(diphenylphosphanyl)-1,1 -binaphthyl dioxide (9, BINAPO) as a promoter of the enantioselective allylation of a-hydrazono esters with allyltrichlorosilanes [27], Nakajima reported the first catalytic system for the allylation of aldehydes, in which the use of N,N-diisopropylethylamine and tetrabutylammonium iodide was essential for accelerating the catalytic cycle (Scheme 7.16) [28], For this allylation, y-functionahzed nucleophiles such as cis-y-bromoallyltrichlorosilane could be employed as addressed by Maikov and Kodovsky [29], In addition, 9 could be apphed to the asymmetric ring opening of meso-epoxides with SiCh, as expected from the scope of the chiral bipyridine N,N -dioxide catalysis [30], and could also catalyze the SiCfi-mediated, enanhoselective phosphonylation of aldehydes with trialkyl phosphites [31],... 

The first example of asymmetric catalytic ring-opening of epoxides with sp2-hybridized carbon-centered nucleophiles was reported by Oguni, who demonstrated that phenyllithium and a chiral Schiff base ligand undergo reaction to form a stable system that can be used to catalyze the enantioselective addition of phenyllithium to meso-epoxides (Scheme 7.24) [48]. Oguni proposed that phenyllithium... 

Sekine, A. Ohshima, T. Shibasaki, M. (2002) An enantioselective formal synthesis of 4-demethoxydaunomycin using the catalytic asymmetric ring opening reaction of meso-epoxide with p-anisidine.. Tetrahedron, 58 75-82. 

Highly enantioselective catalytic desymmetrization of meso-epoxides through nucleophihc ring opening was first effectively demonstrated by Nugent, who found that a zirconium trialkanolamine complex catalyzed the addition of azi-dosilanes to meso-epoxides (Scheme 1) [3]. Azide has been the most widely explored nitrogen nucleophile [4,5,6,7], in part due to its utiHty as an amine sur-... 

The LACS system has been successfully applied to asymmetric catalysis. Catalytic asymmetric ring-opening reactions of meso epoxides with aromatic amines proceeded smoothly in the presence of 1 mol% of Sc(DS)3 and 1.2 mol% of chiral bipyridine ligand (3) in water to give P-amino alcohols in high yields with excellent enantioselectivities (Scheme 12.75) [172]. It has been noted that excellent chiral hydrophobic environments have been created in water. 

Moreover, catalytic asymmetric ring-opening reactions of meso-epoxides with aromatic amines also proceeded in the presence of a catalytic amount of bismuth triflate (Bi(OTf)3), chiral bipyridine ligand 7, and sodium dodecylbenzene sulfonate (SDBS) in pure water. The corresponding /3 -amino alcohols were obtained in good yields with high enantioselectivities (Scheme 3.57). ... 

In 2010, a cooperative dual-catalyst system was reported to promote the highly enantioselective fluoride ring opening of various meso epoxides having alkene, ester, and protected amine functionalities. The reactions were conducted with a chiral (Salen)cobalt complex, (-)-tetramisole, benzoyl fluoride as a latent source of fluoride in the presence of HFIP. The efficient catalytic enantioselective reaction is explained by the generation of a (Salen)Co(III) fluoride under the cocatalytic conditions that occurred in good yields with up to 95% ee (Scheme 44.32). Racemic terminal epoxides, such as styrene oxide, were also studied, but they almost exclusively lead to the fluorine in the primary position therefore, the fluorine atom was not introduced on a stereogenic center. 

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